1. Field of the Invention
The present invention relates to Royer oscillators and push-pull converters. More specifically, the present invention relates to an over-current detection circuit for Royer oscillators and push-pull converters.
2. Description of the Related Art
One conventional approach to monitor current in a Royer oscillator is to put a sense resistor in each half of the Royer oscillator. However, this conventional approach needs extra hardware because it requires two sense resistors for a push-pull converter, which also results in additional power loss. Further, this conventional approach has the disadvantages of being inefficient and being sensitive to noise if the sense resistors are selected to have low resistance values in order to mitigate the power loss from the sense resistors carrying a load current of the switching transistors of the Royer oscillator. Typically, when bipolar junction transistors (BJTs) are used as the switching transistors in a Royer oscillator, the sense resistors are connected between an emitter of each of the switching transistors and ground.
Another conventional approach is to add leakage inductance to the transformer of the Royer oscillator (by separating the primary and secondary windings) and to choose switching transistors with correct gains to limit the over-current. This conventional approach needs extra hardware to separate the primary and secondary windings and requires more time to manufacture. In addition, choosing the appropriate switching transistors can be complex and wasteful.
Numerous Royer oscillators are commercially available. However, many Royer oscillator-based circuits do not have short-circuit protection. Further, commercially available Royer oscillators with short-circuit protection have undesirable power loss in the over-current detection circuit.
The conventional approaches have an inherent problem of loss of efficiency because of the necessary addition of one or more sense resistors. In particular, efficiency is lost in the conventional approaches because of power loss in the sense resistor(s). Also, the addition of leakage inductance leads to more complex transformer construction and requires a careful choice of switching transistors, making the conventional approaches cumbersome to manufacture.